The present invention relates to lost circulation materials (LCM), and to spotting pills containing the LCM. More particularly, the invention relates to acid soluble LCM""s, and to spotting pills containing the LCM, preferably to spotting pills having effective rheology and density.
Drilling fluids serve various functions, such as promoting borehole stability, removing drilled cuttings from the wellbore, cooling and lubricating the bit and the drillstring, as well as controlling subsurface pressure. Certain subsurface permeable formations can cause, or lead to, xe2x80x9clost circulation,xe2x80x9d or the loss of whole drilling fluid in quantity to the formation. In such a case, drilling of the well must be stopped and the condition corrected. Examples of such subsurface permeable formations include, but are not necessarily limited to: (1) natural or intrinsic fractures, (2) induced or created fractures; (3) cavernous formations (crevices and channels), and (4) unconsolidated or highly permeable formations (loose gravels).
Lost circulation materials (LCMs), or formation sealing agents, are used to minimize the loss of drilling fluids into subsurface permeable formations by sealing the formation. To prevent blow-out, or the uncontrolled flow of fluids from the formation into the well, a xe2x80x9cpillxe2x80x9d or slug of the LCM is needed which has a density that is similar to that of the drilling fluid used to treat the formation.
In some cases the formations desired to be sealed may be a potential producing zone for hydrocarbons. Unfortunately, if the sealed formation is a producing formation, it may be difficult to subsequently produce hydrocarbons from the damaged zone. LCM""s are needed which permit removal of the seal and allow for full recovery of hydrocarbons from the loss zone.
The present application provides a high fluid loss spotting pill comprising: a carrier fluid; an LCM consisting essentially of an amount and form of acid soluble mineral particulate; said amount and said form being adapted to form a substantially impermeable, acid soluble filtercake upon injection of said composition with said carrier fluid into said wellbore and defluidization. In a preferred embodiment, the high fluid loss spotting pill preferably further comprises a weighting agent and a suspending agent effective to suspend said weighting agent. The quantity of weighting agent preferably is adapted to produce a density substantially the same as the density of a drilling fluid used to drill a formation being treated.